Wear Resistant Coatings For Radial Bearings and Downhole Tools

ABSTRACT

Abrasion resistant coatings useful for improving abrasive wear and/or corrosion resistance in radial bearings and downhole tools exposed to drilling forces as well as abrasive and/or corrosive drilling fluids. An abrasion resistant coating is disposed on at least one surface of a component body to increase the resistance of the component to abrasive wear and corrosion. The abrasion resistant coating includes a plurality of spherical tungsten cobalt carbide particles and a plurality of tungsten carbide particles. At least 65% by volume of the spherical tungsten cobalt carbide particles have a diameter of less than about 25 microns.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of related U.S. ProvisionalApplication Ser. No. 61/794,091 filed on Mar. 15, 2013, titled, “WearResistant Coatings for Radial Bearings and Downhole Tools,” to Robert J.Ferguson and Peter T. Cariveau, the disclosure of which is incorporatedby reference herein in its entirety.

BACKGROUND

Directional drilling for the recovery of hydrocarbons or minerals from asubsurface formation may be carried out using a downhole motor (alsocommonly referred to as a “drilling motor” or “mud motor”), which isincorporated into the drill string above the drill bit. A downhole motormay include a drive shaft and a bearing assembly, among othercomponents.

During operation of the downhole motor, high-pressure drilling fluid maybe used to power the motor. In addition to powering the motor, thedrilling fluid (or drilling mud) provides hydrostatic pressure toprevent formation fluids from entering the wellbore; cools andlubricates drill string components and the drill bit; and lifts cuttingsaway from the drill bit, among other functions. Various drilling mudsmay be used for specific purposes during drilling operations and oftencontain corrosive chemicals as well as various sized particles toperform their intended task(s).

In recent years, downhole motors have been introduced that generate veryhigh-torque. These include “even-wall” stators such as the ERT seriesoffered by Robbins & Myers and hard rubber (HR) stators such as thoseoffered by Dyna-Drill. Higher torque results from the ability of thesepower sections to withstand higher operating pressures and pressuredrops. The bearing(s) used in the universal joints as drive elements totransmit torque must endure high loads and a fretting motion, whichcreate point contact and high Hertzian stresses that may cause themating materials to yield or spall. Also, when used as thrust bearings,ball bearings and their mating thrust seats may suffer galling becausethe thrust balls must be relatively small, because they are positionedunder, and in the same plane with, the drive elements. Spalling andgalling are destructive occurrences that can lead to costly failure ofthe bearings, and thus, of the entire mud motor.

SUMMARY OF THE DISCLOSURE

Numerous components of a drill string including, but not limited to,e.g., bearings of universal joints, are exposed to high stressenvironments during drilling operations. Further, corrosive and abrasivechemicals may be contained in the drilling muds and other fluids presentin, used in, or introduced into a well, wellbore or other subterraneanbore during such drilling operations. The drill string components may becoated with an abrasive and corrosion resistant alloy to extend theiruseful lifetimes and minimize their failure under such conditions.

In one aspect, one or more embodiments disclosed herein relate to adownhole component having a component body with at least one surface. Anabrasion resistant coating may be disposed on the at least one surfaceof the component body. The abrasion resistant coating may contain aplurality of spherical tungsten cobalt carbide particles and a pluralityof tungsten carbide particles. In one or more embodiments, at least 65%by volume of the spherical tungsten cobalt carbide particles have adiameter of less than about 25 microns.

In another aspect, one or more embodiments disclosed herein relate to aradial bearing, e.g., for use in a downhole tool or motor. The radialbearing may have an abrasion resistant coating on a surface thereof. Theabrasion resistant coating may be formed from a plurality of sphericaltungsten cobalt carbide particles and a plurality of tungsten carbideparticles. In one or more embodiments, at least 65% by volume of thespherical tungsten cobalt carbide particles have a diameter of less thanabout 25 microns.

In another aspect, one or more embodiments disclosed herein relate to amethod of manufacturing a downhole component by applying a layer of anabrasion resistant composition to a metal surface of a substrate. Theabrasion resistant composition may include a plurality of sphericaltungsten cobalt carbide particles and a plurality of tungsten carbideparticles. In one or more embodiments, at least 65% by volume of thespherical tungsten cobalt carbide particles have a diameter of less thanabout 25 microns.

In another aspect, one or more embodiments disclosed herein relate to amethod of forming an abrasive resistant coating. The method may compriseadmixing a spherical tungsten cobalt carbide powder with a tungstencarbide powder to form a mixture, with the spherical tungsten cobaltcarbide powder including at least 65% by volume of particles having adiameter of less than about 25 microns; pucking the mixture to form apuck; milling the puck to form a cloth; applying the cloth to asubstrate; and vacuum brazing the cloth to the substrate.

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

BRIEF DESCRIPTION OF DRAWINGS

The FIGURE is a chart illustrating a particle size distribution of anembodiment of the abrasion resistant coatings disclosed herein.

DETAILED DESCRIPTION

One or more embodiments disclosed herein relate to abrasion resistantcoatings useful for improving abrasive wear and corrosion resistance forradial bearings, tools, and other downhole components exposed todrilling forces and abrasive and corrosive drilling fluids.

Abrasion resistant coatings according to embodiments herein may beformed from a mixture of spherical tungsten cobalt carbide particles andtungsten carbide particles. The abrasion resistant coating may include aplurality of spherical tungsten cobalt carbide particles and a pluralityof tungsten carbide particles. In some embodiments, the sphericaltungsten cobalt carbide particles are spherically shaped plasmadensified tungsten cobalt carbide particles. In forming the mixture, theplurality of particles used may be of varied sizes. For example, theparticle size and/or the particle size distribution of the sphericaltungsten cobalt carbide particles may be selected to result in coatingshaving excellent abrasion resistance, e.g., from decreased oxygencontent or decreased mean free path, as will be discussed further below.

In one or more embodiments, at least 65% by volume of the sphericaltungsten cobalt carbide particles have a diameter of less than about 25microns. In some embodiments, greater than 67.5% by volume of thespherical tungsten cobalt carbide particles have a diameter of less thanabout 25 microns. Further, in some embodiments, greater than 70%, 72.5%,or 75% by volume of the spherical tungsten cobalt carbide particles havea diameter of less than about 25 microns.

In one or more embodiments, less than 5% by volume of the sphericaltungsten cobalt carbide particles have a diameter of greater than about35 microns. In some embodiments, less than 5% by volume of the sphericaltungsten cobalt carbide particles have a diameter of greater than about30 microns. In one or more embodiments, less than 30% by volume of thespherical tungsten cobalt carbide particles have a diameter of greaterthan about 25 microns but less than about 30 microns, while in someembodiments, less than 25%, less than 20%, or less than 15% by volume ofthe spherical tungsten cobalt carbide particles have a diameter ofgreater than about 25 microns.

In one or more embodiments, less than 4% by volume of spherical tungstencobalt carbide particles have a diameter of greater than about 35 orabout 30 microns. In some embodiments, less than 3% by volume ofspherical tungsten cobalt carbide particles have a diameter of greaterthan about 35 or about 30 microns. Further, in some embodiments, lessthan 2.5% by volume of spherical tungsten cobalt carbide particles havea diameter of greater than about 35 or about 30 microns. Further still,in some embodiments, less than 2% by volume of spherical tungsten cobaltcarbide particles have a diameter of greater than about 35 or about 30microns. Furthermore, in some embodiments, less than 1% by volume ofspherical tungsten cobalt carbide particles has a diameter of greaterthan about 35 or about 30 microns.

In addition to limiting the number of large particles used to form thecoating, limiting the number of small spherical tungsten cobalt carbideparticles used to form the coating may also be beneficial. In one ormore embodiments, less than 5% by volume of spherical tungsten cobaltcarbide particles have a diameter of less than about 5 microns. In someembodiments, less than 5% by volume of the spherical tungsten cobaltcarbide particles have a diameter of less than about 7 microns. Further,in some embodiments, less than 5% by volume of the spherical tungstencobalt carbide particles have a diameter of less than about 9 microns.Further, in some embodiments, less than 3% by volume of sphericaltungsten cobalt carbide particles have a diameter of less than about 5,about 7, or about 9 microns. Further, in some embodiments, less than2.5% by volume of spherical tungsten cobalt carbide particles have adiameter of less than about 5, about 7, or about 9 microns. Further, insome embodiments, less than 2% by volume of spherical tungsten cobaltcarbide particles have a diameter of less than about 5, about 7, orabout 9 microns in other embodiments. Further still, in someembodiments, less than 1% by volume of spherical tungsten cobalt carbideparticles have a diameter of less than about 5, about 7, or about 9microns. Furthermore, in some embodiments, essentially no sphericaltungsten cobalt carbide particles have a diameter of less than about 5microns.

The particle size distribution of the spherical tungsten cobalt carbideparticles is less than about 1.5 in some embodiments; less than about1.4 in other embodiments; less than about 1.3 in other embodiments; andless than about 1.2 in still other embodiments. In one or more otherembodiments, the particle size distribution of the spherical tungstencobalt carbide particles is less than about 1.1.

In some embodiments, the spherical tungsten cobalt carbide particleshave a particle size distribution having a D₅₀ (based on volume percent)in the range from about 12 to about 24 microns, such as a D₅₀ in therange from about 13 to about 20 microns or a D₅₀ in the range from about14 to about 18 microns. In some embodiments, essentially no sphericaltungsten cobalt carbide particles have a diameter of less than about 5microns and essentially no spherical tungsten cobalt carbide particleshave a diameter of greater than about 38 microns.

When forming the coatings, the spherical tungsten cobalt carbideparticles and the plurality of tungsten carbide particles may be used ata weight ratio of the spherical tungsten cobalt carbide particles to theplurality of tungsten carbide particles in the range from about 50:50 toabout 90:10. In other embodiments, the weight ratio of the sphericaltungsten cobalt carbide particles to the plurality of tungsten carbideparticles may be in the range from about 55:45 to 88:12; and yet inother embodiments, in the range from about 60:40, 65:35, or 70:30 toabout 75:25 or 80:20.

By restricting the particle size of the spherical tungsten cobaltcarbide particles as described above, the particles may haveadvantageously low initial oxygen content. In one or more embodiments,prior to formation of the abrasion resistant coating, the sphericaltungsten cobalt carbide particles may have an oxygen content of lessthan about 300 ppm by weight; less than 250 ppm by weight; less than 225ppm by weight; or even less than 200 ppm by weight. Excessive oxygen maycause beading, for example, and may reduce the contact angle during thebrazing process. For particle mixtures having high oxygen content, suchas those having an oxygen content greater than 350 ppm or 400 ppm byweight, vacuum baking may be used to decrease the oxygen content to amore desirable range. Advantageously, selection of particle sizedistributions as detailed above may allow abrasion resistant coatingsherein to be formed without a vacuum bakeout of the particles todecrease oxygen content, saving both time and operating expense.Further, elimination of a vacuum bakeout step may result in improvedproduct consistency.

With regard to the tungsten carbide particles, the tungsten carbideparticles may include at least one of monocrystalline tungsten carbide,cast tungsten carbide, macrocrystalline tungsten carbide, or a eutecticmixture of WC and W₂C. In some embodiments, the tungsten carbideparticles are spherical. In other embodiments, the tungsten carbideparticles are irregularly shaped, i.e., non-spherical.

An average particle size of the tungsten carbide particles is generallyselected to be less than an average particle size of the sphericaltungsten cobalt carbide particles. For example, the average particlesize for the tungsten carbide particles may be in the range from about0.1 to about 10 microns, such as in the range from a lower limit ofabout 0.5, 1, 1.5 2, 2.5, or 3 microns to an upper limit of about 1.5,2, 2.5, 3, 3.5, 4, or 5 microns. An average particles size D₉₀ of thetungsten carbide particles may be less than about 10 microns in someembodiments, and the tungsten carbide particles may have an averageparticle size D₅₀ in the range from about 1.2 to about 2.8 microns, suchas in the range from about 1.4 to about 2 microns.

In one or more embodiments, a particle size distribution of a mixture ofthe tungsten carbide particles and the spherical tungsten cobalt carbideparticles is bimodal. For example, in some embodiments the particle sizedistribution of the mixture of tungsten carbide particles and thespherical tungsten cobalt carbide particles may be similar to that asillustrated in the FIGURE. Overall, the mixture may be selected suchthat greater than about 95% of the particles have a particle size ofless than about 35, 30, or 25 microns in various embodiments.

The spherical powders and the size ranges used in one or moreembodiments disclosed herein may allow for improved flow and particlepacking during pucking and brazing processes. The bimodal particle sizedistributions in one or more embodiments disclosed herein may allow forthe small irregular tungsten carbide particles to fill the large poresleft by the larger spherical tungsten cobalt carbide particles. Limitingthe maximum particle size may thus improve wear resistance by removingweak particles that may fracture and cause defects in the material.Further, limiting the large particles significantly improves theuniformity and packing of the particles and may allow a largerpercentage of the tungsten cobalt carbide material to be added to thematrix mixture without disrupting the particle packing and wearresistance. Overall, this leads to a much higher density tungsten cobaltcarbide reinforced material.

Restricting the particle size distribution and the maximum particle sizeof the spherical tungsten cobalt carbide particles may result in adecrease in the mean free path for the braze infiltrate as compared tomixtures including any significant quantity of particles greater thanabout 35 microns in size. In other words, the particle size selectionmay restrict the mean free path between carbide particles and sinteredmasses of carbide. The resulting reduction in mean free path, ascompared to mixtures including larger particles, may result in improvedabrasive resistance, thereby reducing the rate at which erosion andabrasive wear may occur. The presence of a larger mean free path andbraze accumulation will result in erosion and abrasive wear at a muchfaster rate than adjacent carbide masses. Further, the use of sphericaltungsten cobalt carbide particles may reduce the localized stressconcentration at the surface of sintered masses. Thus, proper selectionof particle size and particle size distribution according to one or moreembodiments disclosed herein may provide for superior abrasion resistantcoatings.

In some embodiments, the abrasion resistant coating has a mean freepath, as measured using image analysis and Scanning Electron Microscopy(SEM), between spherical tungsten cobalt carbide particles of less thanabout 15 microns. In other embodiments, the abrasion resistant coatinghas a mean free path between spherical tungsten cobalt carbide particlesof less than about 10 microns. In other embodiments, the abrasionresistant coating has a mean free path between spherical tungsten cobaltcarbide particles of less than about 9 microns. In other embodiments,the abrasion resistant coating has a mean free path between sphericaltungsten cobalt carbide particles of less than about 8 microns. In otherembodiments, the abrasion resistant coating has a mean free path betweenspherical tungsten cobalt carbide particles of less than about 7microns. In other embodiments, the abrasion resistant coating has a meanfree path between spherical tungsten cobalt carbide particles of lessthan about 6 microns in other embodiments. In other embodiments, theabrasion resistant coating has a mean free path between sphericaltungsten cobalt carbide particles of less than about 5 microns. In yetother embodiments, the abrasion resistant coating has a mean free pathbetween spherical tungsten cobalt carbide particles of less than about4, 3, or even 2 microns.

As noted above, vacuum baking of the particles may be used to reduceaverage particle oxygen content. Heating of the particles during vacuumbaking may result in sintering of some particles, which negativelyimpacts mean free path. Mean free path may thus advantageously beimproved by proper selection of particle size and particle sizedistributions according to one or more embodiments herein.

The mixture of particles described above may be used to form abrasionresistant coatings having an abrasive resistance factor of at least 150.The abrasion resistance factor (ARF) may be determined by measuring theweight loss of the coating according to ASTM G65 method A, and thedensity of the coating according to ASTM B311. The weight loss isconverted to a volume loss by dividing the weight loss by the density ofthe coating. This volume loss is adjusted to account for diameter changeof the rubber wheel during the test. The abrasive resistance factor isthen calculated by taking the inverse of the adjusted volume loss times1000. Abrasion resistant coatings, according to one or more embodimentsherein, may have an ARF of at least 160; an ARF of at least 170; an ARFof at least 180; an ARF of at least 190; or an ARF of at least 200.Abrasion resistant coatings, according to one or more embodimentsherein, may have an ARF in the range from about 160 to about 220 or inthe range from about 175 to about 200.

Production of spherical tungsten cobalt carbide particles may result inparticles outside of the desired range of particles described above. Insome embodiments, tungsten cobalt carbide particles may be sieved,ultrasonically sieved, or air classified to result in the desiredparticle size range and particle size distribution.

The abrasion resistant coatings described above may be applied to adrilling component, such as a radial bearing, to form a coated drillingcomponent for use in drilling or other operations that may be performeddownhole. For example, the abrasion resistant coatings described abovemay be applied to a wear surface of a radial bearing or other portionsof a drilling component to provide a drilling component that hasabrasion and wear resistance.

To facilitate application of the abrasion resistant coatings, thetungsten carbide particles and the spherical tungsten cobalt carbideparticles may be pre-mixed and/or milled with a ball mill, TURBULA, orother means. The mixture of particles may then be joined together toform a puck; for example, the pucking process may include joining theparticles together by a web-like structure formed by one or morepolymeric materials, such as polytetrafluoroethylene (PTFE).

The resulting puck may then be milled into a thin flexible membrane orcloth. The thickness of the cloth selected may vary depending upon theunderlying substrate, such as an iron metal or alloy, among others, aswell as the depth of capillary action of the infiltrate to the selectedunderlying substrate. The flexible cloth may then be applied to asubstrate and may readily conform to the shape of the substrate. Thecloth may then be cut to shape and applied with a low temperatureadhesive, if desired. Optionally, another cloth, such as a clothcontaining a braze material powder, may then be applied onto the layerof cloth formed according to one or more embodiments disclosed herein.

Once the cloth is applied, the temperature of the cloth layers and thesurface of the substrate may be increased to brazing temperatures toeffect the metallurgical bonding of the cloth layer(s) with thesubstrate material. The infiltration brazing process may be performed,for example, using a vacuum furnace with an inert gas atmosphere topreclude degradation of complex carbides at brazing temperatures, whichmay be in the range from about 500° C. to about 1200° C. The brazedproduct may then be ground to produce a controlled finish without abuseof the abrasion resistant coating.

The brazing process may result in a change in physical properties of theunderlying substrate. In some embodiments, the brazed product may beheat treated to restore the grain structure and mechanical properties ofthe substrate altered by the elevated temperatures during vacuumbrazing.

As described above, abrasion resistant coatings according to one or moreembodiments herein may be used to enhance the wear resistance ofcomponents that are used in drilling or downhole operations, where suchcomponents may be exposed to drilling muds and other fluids containingabrasive and corrosive constituents. In some embodiments, the abrasionresistant coatings as described above may be applied to radial bearings,thrust bearings, universal joints, and transmissions, among other suchcomponents.

Although only a few example embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications are possible in the example embodiments without materiallydeparting from the disclosure. Accordingly, all such modifications areintended to be included within the scope of this disclosure. In theclaims, means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents, but also equivalent structures. Thus, although anail and a screw may not be structural equivalents in that a nailemploys a cylindrical surface to secure wooden parts together, whereas ascrew employs a helical surface, in the environment of fastening woodenparts, a nail and a screw may be equivalent structures. It is theexpress intention of the applicant not to invoke means plus functiontreatment for any limitations of any of the claims herein, except forthose in which the claim expressly uses the words ‘means for’ togetherwith an associated function.

What is claimed is:
 1. A downhole component, comprising: a componentbody having at least one surface; and an abrasion resistant coatingdisposed on the at least one surface of the component body, the abrasionresistant coating including a plurality of spherical tungsten cobaltcarbide particles and a plurality of tungsten carbide particles; whereinat least 65% by volume of the spherical tungsten cobalt carbideparticles have a diameter of less than about 25 microns.
 2. The downholecomponent of claim 1, wherein the spherical tungsten cobalt carbideparticles in the abrasion resistant coating have a mean free path ofless than about 15 microns, as measured using image analysis andScanning Electron Microscopy (SEM).
 3. The downhole component of claim1, wherein the spherical tungsten cobalt carbide particles comprise lessthan 5% by volume of particles having a diameter of less than about 5microns.
 4. The downhole component of claim 3, wherein the sphericaltungsten cobalt carbide particles comprises essentially no particleshaving a diameter of less than about 5 microns and essentially noparticles having a diameter greater than about 38 microns.
 5. Thedownhole component of claim 1, wherein the spherical tungsten cobaltcarbide particles are spherically shaped plasma densified tungstencobalt carbide particles.
 6. The downhole component of claim 1, whereinthe spherical tungsten cobalt carbide particles have a particle size D₅₀in the range from about 12 to about 24 microns.
 7. The downholecomponent of claim 1, wherein the abrasion resistant coating has anabrasive resistance factor of at least
 150. 8. The downhole component ofclaim 1, wherein a weight ratio of the spherical tungsten cobalt carbideparticles to the plurality of tungsten carbide particles is in the rangefrom about 50:50 to about 90:10.
 9. The downhole component of claim 1,wherein the spherical tungsten cobalt carbide particles have an oxygencontent of less than about 300 ppm by weight.
 10. The downhole componentof claim 1, wherein an average particle size D₉₀ of the tungsten carbideparticles is less than about 10 microns.
 11. The downhole component ofclaim 1, wherein the tungsten carbide particles comprise at least one ofmonocrystalline tungsten carbide, cast tungsten carbide,macrocrystalline tungsten carbide, or a eutectic mixture of WC and W₂C.12. The downhole component of claim 1, wherein the tungsten carbideparticles are spherical.
 13. The downhole component of claim 1, whereina particle size distribution of a mixture of the tungsten carbideparticles and the spherical tungsten cobalt carbide particles isbimodal.
 14. The downhole component of claim 1, wherein the downholecomponent is a radial bearing.
 15. A method of manufacturing a downholecomponent, comprising: applying a layer of an abrasion resistantcomposition to a metal surface of a substrate, the abrasion resistantcomposition comprising: a plurality of spherical tungsten cobalt carbideparticles and a plurality of tungsten carbide particles; wherein atleast 65% by volume of the spherical tungsten cobalt carbide particleshave a diameter of less than about 25 microns.
 16. The method of claim15, further comprising heating the abrasion resistant composition and atleast the surface of the substrate to effect metallurgical bonding ofthe abrasion resistant composition with the substrate.
 17. A method offorming an abrasive resistant coating, comprising: admixing a sphericaltungsten cobalt carbide powder with a tungsten carbide powder to form amixture, wherein the spherical tungsten cobalt carbide powder comprisesat least 65% by volume of particles having a diameter of less than about25 microns; pucking the mixture to form a puck; milling the puck to forma cloth; applying the cloth to a substrate; and vacuum brazing the clothto the substrate.
 18. The method of claim 17, further comprising atleast one of: ultrasonic sieving or air classifying a mixture oftungsten cobalt carbide particles to recover a fraction of tungstencobalt carbide particles where at least 65% by volume of particleshaving a diameter of less than about 25 microns; mixing the fraction ofspherical tungsten cobalt carbide particles with tungsten carbideparticles; adhering the cloth to the substrate using an adhesivecompound; or applying a second cloth comprising a braze material powderto the cloth.
 19. The method of claim 17, wherein the vacuum brazing iscarried out under an inert atmosphere.
 20. The method of claim 17,wherein the process does not include vacuum baking of the tungstencobalt carbide particles to reduce an oxygen content thereof.